1. Field of the Invention
This invention is related to water clarifying systems in general and is specifically directed to a high efficiency filter for mechanically removing suspended solids and fine particles from an aqueous media to obtain a clear effluent.
2. Description of the Prior Art
In many water/wastewater treatment operations, there are standardized quality criteria to be met by the treatment process as well as the equipment involved. These criteria limit the final content of a constituent or pollutant in terms of concentration and the limit on total suspended solids (TSS) for clarity. The TSS desirable is usually limited to a zero-10 ppm range. It is common to find the pollutant discharge in form of suspended solids.
Typically, filters are employed to achieve the above objectives if a mechanical clarifier or gravity settling system cannot meet the stated limits. A variety of filters have been in use for many years, with several types having been developed over the last twenty years. In particular, sand and gravel filters, fine sand filters, charcoal/activated carbon/anthracite filters, diatomaceous earth filters and filament wound/paper/cloth or bag-type filters have been used with varying degrees of success to reduce the TSS in an aqueous media as a post-clarification process. In some cases, these filters are used in combination to further improve results.
Most of the filter systems of the prior art depend on a hydraulic gradient to provide filtration and, once the pressure loss is too high for satisfactory operation, a backwash system is required to restore the filter to operating condition. In many cases, restoration can be achieved only by complete replacement of the filter media. The backwash system for restoring filter capacity calls for a supply of clean filtrate or a clean water source, a pump, instrumentation and a control system to accomplish the task. The backwash cannot be discharged into the sewer if the constituents or pollutants being removed are regulated by effluent guidelines in the same manner as the main wastewater treatment operation.
If replacement of the media is the chosen method of restoring filtration capacity, the cost involved is usually quite high. The media disposal also poses a problem for many industries as regulations become applicable to the waste media product.
Pressure filter systems impose similar restrictions on cost, space and resource requirements and, in the case of diatomaceous earth filters, create the largest quantity of solid waste disposal problem for any filter use.
Examples of mechanical or pressure type filter systems of the prior art are illustrated in a number of U.S. patents. By way of example, U.S. Pat. No. 4,014,767 entitled "Self-Contained Waste Disposal System Including Self-Cleaning Filter," issued to F. Schmidt on Mar. 29, 1977 shows a series of absorbent plates for wastewater treatment, but it is strictly a gravity system. U.S. Pat. No. 4,025,430 entitled "Removal of Metal Ions From Waste Water," issued to R. Pagel on Mar. 24, 1977, is directed to removal of metal ions from wastewater by adjusting the pH. U.S. Pat. No. 4,053,386 entitled "Electrolytic Filter for Electrolytically Filtering and Recovering Metals From Colloidal Suspensions," issued to F. Schmidt on Oct. 11, 1977, discloses an electrolytic filter which includes perforated electrodes wherein the flocculents are charged and then attracted to and trapped by the filter. U.S. Pat. No. 4,189,381 entitled "Waste Water Treatment," issued to J. Laferty, et al. on Feb. 19, 1980, discloses an electrolytic filter which includes perforated conducting electrodes where in the flocculents are charged and then trapped by the filter. U.S. Pat. No. 4,923,600 entitled "Water Clarification System Adapted For Removing Particulate Matter of Greater than a Predetermined Size," issued to M. Krofta on May 8, 1990, discloses a system where the flocculent is in an electroflotation state and may be removed by skimming.